text:
How does gross weight affect the Minimum Controllable Airspeed (Vmc)?
I am about to get my MEL added to my CFI, and I cannot get my head around the multiple explanations for how gross weight affects Vmc.
The accepted answer is that The higher the gross weight, the lower is the Vmc.
I have been proffered two contradictory explanations, from both internet articles, manufacturer documents, and other CFIs, both of which seem to me (I have an MSME masters degree in Aero) to be flawed.

That because the aircraft is slightly banked into the direction of the good engine, the horizontal component of Lift (HCL) opposes the yaw from the rudder, thus allowing the aircraft to slow to a lower airspeed before full rudder authority is required to counteract the yaw from the operating engine.
This is wrong, because if you're in a bank, the HCL (by definition, it is HORIZONTAL!), is no longer lined up with the lateral axis of the aircraft. It is misaligned by exactly the bank angle, so, although there is a component of the HCL opposing the yaw force from the rudder, there is an exactly equal and compensating component of the Vertical Component of Lift (VCL) that will be augmenting the Yaw force.  This argument is bogus.

I mean if you think about it simpler, the Lift vector is always, ALWAYS, perpendicular to the wings, so that any effect of Lift along the lateral axis (parallel with yaw forces), must necessarily be zero.
The fact that is not aligned with the earth horizon is irrelevant.

The other rationale I have been presented with is that as the gross weight increases, the resistance to motion (Engineers would call this rotational inertia) increases, and makes the aircraft more stable. This is true, but it is an argument about dynamic stability, not about static stability. In other words, this affects the aircrafts resistance to changes in yaw/sideslip angle. Vmc is about static stability, i.e., at what airspeed does the aircraft, in a static, (unchanging) zero sideslip angle, require full rudder defection to hold the aircraft (STATICALLY) at that zero sideslip angle against all the yaw forces being produced by all the factors resulting from Asymmetric thrust?
So this argument or rationale also seems to be incorrect to me.

Where is the flaw in this reasoning?
By the way, the only effect of Gross weight on Vmc that I can think of is the obvious one, The higher the gross weight, the greater the Angle of Attack required to hold 1 G (Level flight), and obviously, both P-Factor and adverse yaw increases with AOA. So the higher the Gross weight, the greater the P-Factor, and the greater the yaw-induced aerodynamic effects of the asymmetric thrust. So, if this logic is correct, Higher Gross weight means Higher Vmc, not Lower.

How do you add a Minimum Equipment List to your CFI?

I think your objection to #2 is exactly correct, and your #1 is where the misunderstanding may lie.
The point of VMCA is essentially to maintain a constant heading, and when you have no more rudder authority to make that happen, you're there -- and any slower, with slightly less rudder authority, your heading starts to change in the direction of the dead engine.  With no bank, it's all rudder; the lift from the wings doesn't tend to move the nose in any direction.  With bank, there is now a component of the lift from the wings that does tend to affect heading (which is the dynamic of banking when you turn -- the heading change comes from the lift created by the wings, not from the lift generated by the rudder).
If you are banking into the good engine, that component of lift tends to change your heading toward the good engine and away from the failed engine.  Since the asymmetric thrust is working to change your heading toward the failed engine while you hold rudder to oppose that change, you now have the component of lift from the wings that is assisting your rudder.
If you consider a case of symmetric thrust, you can hold a heading with right wing down and left rudder or vice versa; the lift from the wings is working to change your heading to the right, and your rudder is counteracting that drift. At some point, with enough bank, you run out of rudder authority & the airplane will turn, although pretty badly uncoordinated.  With an engine out, you CAN fly straight ahead holding bank into the dead engine, you just need a lot of rudder authority (i.e. lots of speed above VMCA) to hold your heading -- the rudder is fighting both the asymmetric thrust and the component of the wings' lift. And doing that, you'll run out of rudder authority a lot sooner (i.e. at a higher airspeed).  If you switch to bank into the good engine, the component of lift from the wings is now working with you, and that's the usual case for computing and demonstrating VMCA.
I suspect that the confusion on your point #1 comes by conflating horizontal (earth reference) with horizontal (aircraft reference). Hopefully the explanation above separates things out?
And, to bring things back to gross weight, the higher the weight, the greater the lift from the wings, so a Sin(5 degrees) (I think that's right -- LONG time since I took Trig!) component of "more lift" is a greater force to resist heading change than that same component of "less lift" with a lighter aircraft.  The other forces involved in the balance, the asymmetric thrust and the rudder force, are independent of aircraft weight.
Best wishes for your MEL checkride!

But the vertical component of Lift is acting in the opposite direction. i.e., Say the vertical component of Lift is LCos(5 deg). Then the component of that which is acting along the aircraft lateral axis (parallel to the Yaw force) is LCos(5deg)sin(5deg), in the SAME direction as the Yaw force, so it is augmenting the effect of yaw from the Rudder. The exacerbating effect of the HCL is Lsin(5deg), and the component of that which is aligned with the Yaw force is Lsin(5deg) cos(5deg), in exactly the opposite direction. They cancel each other out.

By the way, as I understand it, the reason we are in a bank is because although we need the rudder to attain zero sideslip (to minimize drag and maximize excess thrust), this generates a sideways yaw force, which, uncorrected, will cause the aircraft to turn. We put the aircraft in a bank to counteract this turning force and keep a constant heading.

@CharlesBretana Let's say your left engine is dead. Aircraft wants to yaw left. Rudder is displaced right, pushes tail left, and nose right. You're banking right (into the good engine). The lift from the wings is: all vertical (aircraft reference), mostly vertical(earth reference), some right (earth reference). Which tends to track the nose to the right -- assisting the rudder. The rudder is "pushing (the tail) left" while the wings are "pushing (the nose) right" but they're both pushing the heading in the same direction (right).

Also, NO component of lift from the wings ever generates ANY yaw. Those two components are always perpendicular. The lift from the wings can track the nose, but it doesn't generate yaw. When you talk about a component of lift acting parallel to the yaw force, that's not quite accurate. Your "wing-aligned component of VCL" isn't right -- the LIFT vector has ZERO wing-aligned component. It has a horizontal component in the earth-frame-of-reference, but not in the aircraft frame of reference. Your red & purple arrows will cancel each other out; the blue HCL arrow remains & tracks the nose.

Right - the lift vector CANNOT generate Yaw. That's my whole point here. No matter how much bank you have, ALL Lift is perpendicular to the Yaw vector. What I am describing is just Math to address the argument that the Horizontal component of Lift (HCL) somehow augments and exacerbates the yaw from the rudder, which is the essence of this argument. It can't, because if you want to actually look at it this way, then you also have to look at the effect of the Vertical component of Lift, which (because of the argument you make), must exactly oppose and compensate, for the effect of the HCL.

And as to the "they're both pushing the heading in the same direction (right)." -  No, I don't think so, You may be conflating force and torque. Right rudder creates clockwise torque on the aircraft (as from above), but clockwise torque does not turn the aircraft. With both engines, it would just make it fly in a sideslip. With left engine out, it just counteracts the left yaw from the right engine to allow flight in zero sideslip. Right rudder creates a leftwards force on the aircraft. It pushes the air right, and aircraft Left, which, without the bank, would cause a left, not a right  turn.

The flaw in the reasoning under 1. is that you should not show horizontal and vertical components of lift, but of gravity. You're considering the aircraft reference frame, and should look at gravity alignment with the aircraft axes. This is proportional to sin $\Phi$ and to mass.
What you were doing was breaking the lift vector into earth axis components, then re-breaking the resulting components into aircraft axis components where they already were.

It's  fun to listen to engineers talk about flying airplanes. I know this is a little late for the answer but here we go. It's not the lift, It's the weight. A plane in flight balances at the center of lift, not the center of gravity. As the CG is normally forward of the CL the bank causes the nose to yaw toward Gravity. The more weight vectored toward the live engine with bank the less the rudder has to do. The bank angle is limited because of other considerations. 90* of bank would vector all the weight to oppose yaw. This is the same reason that excess thrust, not more lift, is the force that causes the constant speed climb. Anything that causes less lift to have to be generated by the vertical tail will cause the speed needed to produce that lift to be lower. Changing the weight vector or increasing the vertical tail moment by moving the CG forward will decrease the total lift required to counter the yaw.

Just as a note, answering older questions is fine on Stack Exchange, as long as you're able to add something that hasn't already been said in other answers and you make sure to actually answer the question that is being asked rather than simply providing commentary on existing answers.

@user28842, Aircraft balance aerodynamically about the Center of Lift, they "rotate", inertially, about the CG. Second, I believe that when a body is airborne, the force of gravity is a fictitious force, only necessary in calculations  because we do our calculations in an accelerated frame of reference. The only forces that need be considered  for this issue are the aerodynamic forces, and the asymmetric thrust of the one good engine.

@CharlesBretana “Gravity is a fictitious force” in flight? Some force needs to balance Lift, since the aircraft is often maintaining an altitude rather than accellerating upward at (Lift/Mass) ft/sec/sec for the entire flight...

@RalphJ, Actually no, its is just like Centrifugal "force", in that it is a fiction, a mathematical construct only required to make the calculations correct when using an accelerated frame of reference. Imagine doing the same calculations in outer space, with no gravity, but inside of a giant box that was accelerating under one "G" of thrust. You would be of course have to include one "G" of gravity to get the answer to be correct relative to the frame of reference of the box.

This is same idea as Einstein's famous elevator experiment,   https://www.thegreatcoursesdaily.com/einsteins-experimental-elevator/  where he compared being in outer space, in free fall, and being in a free-falling elevator... They are not similar, they are the same, because they are both in a zero-G or non-accelerating frame of reference,

After Einsten, we know that Newton's theory of Gravitation, which posits that Gravity is a force, although very accurate most of the time, is wrong.  In Einstein's theory of gravity, gravity is not a force, it is a distortion or warping of the structure of space and time which causes all objects (even massless photons) to appear to travel in curved paths to us as they follow what are straight lines in this warped space-time.

Then why is it every time the engine stops I end up on the ground. To the point the same (force) that requires downward lift of the horizontal tail when the lateral axis is parallel to the earths horizon acts in yaw when the vertical axis is parallel to the horizon

Well, let’s consider the problem in detail.
Assumptions:
the aircraft is a light twin under 6,000lbs GTOW powered by reciprocating engines.
Engines and propellers are of a tractor configuration, mounted on pylons forward of the wing leading edges.  Engines are not geared to counter rotate and turn clockwise from the pilot’s perspective; left engine is the critical engine.
The center of lift is aft of the center of gravity for the entire approved CG Range.
Factors affecting Vmc is the position of the CG as this affects the length of the moment arm for the rudder to counteract the vertical moment caused by the asymmetric thrust loading as a consequence of a critical engine failure.  Aft most CG is the worst case.
Asymmetric thrust moment will be a sum of the moments caused by the position of the line of thrust (engine crankshaft) relative to the lateral position of the aircraft CG (airplane centerline) and the thrust aysymmetry caused by P Factor over the propeller disc.  Worst case is right at takeoff power at critical AOA.
The horizontal component of lift HCL is used to counteract the lateral drift resulting from the yawing force of the rudder.  Regulations and good operating practices limit the amount of bank used to generate this HCL to 5° in order not to diminish the climbing characteristics at low speed with a OEI condition.
Since the airplane will reach the critical AOA at a higher indicated airspeed when at GTOW than at a lower gross weight, it will stall at faster airspeeds than a lightly loaded aircraft would.  But since the force and the corresponding counter moment that the rudder can generate are greater for a higher airspeed than a lower one, the aircraft may stall at or below the minimum control speed in this case.  At a lower loading the aircraft will stall at a slower airspeed, but the rudder will have a diminished effectiveness here.  This may result in a case where Vmc may be reached at or above the stall speed for the aircraft.  The wings as well are generating greater lift for an AOA at higher speeds, so the HCL can more effectively counter the rudder loads at higher airspeeds than at lower ones without exceeding the 5° bank limit for this.
In truth, there is no one set Minimum Control Speed; it varies based upon a number of factors such as aircraft type and configuration, density altitude, gross weight, etc.  The value of Red Line is based upon certain configurations during flight testing.  In practice, minimum control speed will be identified when you encounter any of these three conditions with OEI and the propeller windmilling:

Loss of directional (yaw) control.
Maximum rudder deflection in the direction of the operating engine.
Buffet just prior to aerodynamic stall.

Recognizing this condition and being able to articulate that to a student pilot next to you is what an examiner is going to want you to demonstrate on your checkride and is probably going to be the limit of the knowledge they expect about Vmc.

Gravity has no aerodynamic effect on an aircraft. Vmc is an aerodynamic effect. Gravity has no aerodynamic effect on an aircraft. Only aerodynamic effects can affect Vmc.

Secondly, the rudder is not the only aerodynamic surface creating lateral lift. The fuselage can create lateral lift. That's why you need a right bank to counteract the left turn induced by Left sideslip when landing in a crab in a right crosswind. Left rudder does create right lift, but it puts the fuselage into a left sideslip (to line up with the runway), and the left sideslip creates a larger lift to the left. With left engine out, right rudder only brings the fuselage back to zero sideslip, - the only lateral lift is from the rudder, to the left. So the right bank counteracts that.

And my point in breaking the lift into components twice is just to show that this technique is indeed, pointless. The Lift is always perpendicular to the lateral axis of the aircraft, so Breaking it up into Horizontal and vertical components (relative to the horizon), is meaningless, since these are not aligned with the aircraft. And breaking those up into aircraft aligned components, just reverses the process and shows that there is zero effect along the lateral axis from any amount of lift, no matter the gross weight.

Charles, you're getting tangled up here with your information and it's causing you to miss the real facts.  The HCL is necessary in this problem as it is the force causing the aircraft to 1) turn or 2) counter the lateral lift force from the vertical fin and rudder during to prevent lateral drift of the aircraft.  You use right rudder in the event of a left engine failure to counter the torque generated by the asymmetrical thrust (do a sum of moments about the CG with an OEI and this becomes clear).

Carlo,I'm sorry, but I don't believe I am. The HCL, as defined, is the component of Lift parallel with the Horizon, due to the bank, and yes, it, alone, would cause the aircraft to turn to the right. I fully understand that. But The aircraft is NOT turning right, so something else must be causing it to remain on a constant heading. That something is the leftwards Lift generated by the right rudder. That's why we establish the right bank - to stop the left turn that the rudder would induce. But what does this have to do with Vmc??!!

And yes, you are also correct that the right rudder counteracts the left yaw due to a OEI, and right, if you do the sum of moments this is clear. But again, what does this fact have to do with the HCL? The HCL should not enter into the sum of moments for Yaw at all. If you did include it, to be accurate, you should also include the effect of the Vertical Component of Lift on Yaw, which, being exactly equal and opposite, cancels out the effect of the HCL. Which if you think about it makes sense, since Lift is ALWAYS perpendicular to the Yaw and therefore can Have NO effect on Yaw moment.

The HCL does not enter into the sun of moments, but it does enter into the sum of forces and is going to be equal to the lateral force of the rudder as seen through a sum of forces

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Under what conditions can a flight continue beyond the point of in-flight re-planning?
I'm studying ICAO Annex 6, but I am confused a little bit about the paragraph below:

6-2.2.3.4.2(b)
A flight to be conducted in accordance with the instrument flight
rules shall not take off or continue beyond the point of in-flight
re-planning unless at the aerodrome of intended landing or at each
alternate aerodrome to be selected in compliance with 2.2.3.5, current
meteorological reports or a combination of current reports and
forecasts indicate that the meteorological conditions will be, at the
estimated time of use, at or above the aerodrome operating minima for
that operation.

Here I have simple question about following situations.

Can I continue flight at the point of in-flight re-planning if:
"destination airport WX > minima" & "alternate airport WX < minima"

Can I continue flight at the point of in-flight re-planning if:
"destination airport WX < minima" & "alternate airport WX > minima"

Annex 6 of....? the Convention on International Civil Aviation (link)

Hi, and welcome to Aviation.SE.  Whenever you ask about rules and regulations, it's important to state the jurisdiction since this is an international site.  We have tags for the major jurisdictions such as EASA, CAA, FAA etc.

it’s just a complicated way of saying: you are not allowed to begin an IFR flight either from the ground (“shall not take off”) nor can you file a new one in the air (“continue beyond the point of in-flight re-planning”) unless some weather conditions are met at the destination and nominated alternate(s).
I other words the “point of in-flight re-planning” is not a decision point, it’s just: the point where we would like to file (re-plan) a new flight plan (in-flight).
And the conditions are the same wether you are on the ground or already flying: either (destination WX > operational minima) or (ALL nominated and required alternates > planning minima)
note that (depending on jurisdiction) most of the times a minimum 2 alternates are required if destination WX < operational minima.

Can I continue flight at the point of in-flight re-planning if:
  "destination APO WX > minima" & "alternate APO WX < minima"

if destination > minima, under specific circumstances you might not require an alternate. if still required, it must be nominated and above the planning minima. So answer : probably no.

Can I continue flight at the point of in-flight re-planning if:
  "destination APO WX < minima" & "alternate APO WX > minima"

if destination < minima, you will most likely require 2 nominated alternates and the must BOTH be above planning minima. Shory answer: yes

This means that we could take off even though the weather forecast indicates the weather at destination and/or alternates is below required minima, providing we nominate a decision point, with a suitable enroute alternate. If, on arriving at the destination point,the weather forecast at the destination remains below the minima, the pilot must divert to the nominated enroute alternate. So you can take off and continue until that point and if you see the weather at your destination is still below minima then you have to divert to your alternate, but if the weather at your destination will be above minima and the weather at your alternate won't be above minima, then you have to change your alternate or enroute alternate aerodrome because:

All IFR flight have must have at least one alternate aerodrome
Decision point procedure is also need an alternate (can be enroute)

This was Decision Point Procedure.
If you don't have any alternate available, then you must apply with Pre-Determinded Point Procedure.

I’m afraid the question has nothing to do with the Decision Point, which is a technique involving contingency fuel and has no bearing on the weather at destination. Pilots are free to continue flying to any airport regardless of weather conditions. Wether they can then begin/attempt an approach is a different issue.

also, there are cases when an IFR flight does not require any alternate. Can you name two of them? :-p

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
Is it practical to intentionally stall an aircraft to execute a fast, controlled descent?
An MD-11 had an onboard fire, but had to request more flying distance at least partly to execute a safe descent (and to dump fuel). It ended in tragedy.
In another accident, an A330 descended 30,000 feet in three minutes, in control (or at least in a recoverable state) during a stall.
Right now, airplanes in general, and particularly large jets, seem to be limited to 8000 fpm. So, I am wondering, can an intentional stall really accelerate this descent in a safe manner? The very high drag would keep the airplane from overspeeding, and there's no need to certify things like thrust reversers for deployment during flight. Heck - it could even be used to speed up the approach phase of a landing, saving time and airspace.

Comments are not for extended discussion; this conversation has been moved to chat.

Just a fun fact: On paraglides, we consider a full stall a reset maneuver: If your wing  is hopelessly entangled, you can go into a stall, make your wing collapse, and attempt to reopen it in a clean state. Well, don't try this at home or in commercial aviation.

In a dogfight emergency you can use it bleed speed; for instance, if you want to be behind the opponent instead of in front of them. You need vectored thrust, and your wings must be designed not to come off though ;-).

But I love the idea to put a jet liner in full stall during an airport approach. "Ladies and Gentlemen, the funny feeling in your stomach will be fully intentional. We will be in full control of the aircraft at all times. We suggest you focus on your movie for the next two minutes. No, you cannot go to the bathroom now."

@Peter-ReinstateMonica I have read WWII fighter pilot recounts of using stalls and spins to shake a fighter on their six. Certainly no vectored thrust there, just supreme mastery of their aircraft. ;-)

Aaaaaaaand I have 4 downvotes. What's going on?

Mail pilots used to spin through cloud decks before the days of instrument flight.  Does that count as practical?

@acpilot that probably fits both criteria

Citations of the situations being described would be helpful.

@IanKemp is that addressed to me?

@Abdullah Yes - even if it's just links to the situations in question, editing them into your question will provide more context for readers who wish to explore the subject further.

@IanKemp I won't give the flight numbers, but I'll link to their Wikipedia articles.

@Abdullah Perfect, thank you!

You don’t need a new technique
You don’t normally stall jetliners.  And in a crisis the last thing you want to do is learn a new technique.
Besides, they already have a trained practice for descending jetliners very quickly.  It’s used for loss of cabin pressure.  While the procedure normally levels at 10,000’/3000m, it could certainly be extended.
Anyway, descent time has not been the failure point
When you look at fire-on-airplane tragedies, the pinch point has not been inability to make bare-minimum time to landing/evac.  The problem has been pilots overestimating the time they have available.
Look at the UPS Air tragedy and go figure where they were in the airspace at the first sign of fire.  The closest large airport with facilities was an Iranian military base on a nearby island.  The second closest large field was Doha, Qatar.  They decided to return to Dubai.
Now, think about that decision-making. Iranian military base with a US-flagged airliner technically in the US military reserve? Yeah, not an ideal situation.  Doha, this was obviously a maintenance problem and they didn’t have a maintenance base there.  Dubai was only, what, 10 minutes further.
And of course, as is very typical in these flights, they continued moving away from Dubai after the first sign of trouble, until they chased the problem a bit and concluded yeah, they really did need to return.
So we have a number of potential saves on the table, but they did a careful analysis and made a more preferential choice given a number of factors. The time spent making those choices sealed their fate.
Then we look at the flight that went down off Halifax. Again, the first sign of trouble, and indeed the second sign of definite fire, happened fairly early - and they still had a variety of divert airports (some not very good choices for a fuel-heavy jetliner).  They chose Halifax, which could’ve worked if they had realized they were on the clock, but then they piddle-diddled in the air with a great deal of time-wasting communications and procedural stuff, until they were overcome.
Why not just beeline for the nearest airport?
The problem is that, early on, the signs are ambiguous.  Those early signs are often seen without an ensuing fire.  So the pilots are concerned with being perceived as alarmist or “making the problem up” if it turns out to be nothing special.
And a divert complicates things.  The descent, landing, takeoff, climb and resumption of flight takes fuel that wasn’t allocated, which means the turns-out-to-be-nothing aircraft must buy fuel at the divert airport - where they may not have a supply contract.
Either company or a perhaps non-contract FBO (independent mechanic) qualified on that type must be found and/or flown into that airport, to clear the plane for continued flight.  (If it’s nothing). Meanwhile the added time will put this aircrew “over time” so they will not be able to finish the flight.  New aircrew must come in also.
Likely the most expedient way to get people on their way is for the airline to bring in another heavy, and pay more landing fees at an airport where they do not have a contract, other aircrew called in, etc.  This may take enough time that the airline has to book every hotel in the 3 nearest towns, and find transport for them all, which basically involves getting someone from the local middle school on the phone on a Sunday.
Like the Halifax case, it may involve hundreds of people going through immigration in a country they might not have a visa - heck, it creates another crisis if they land a 300-pax jet at an airport with no Immigration facilities (or a small one sized for 12-passenger rubberband planes).  Remember they “skidded to a stop” on the runway, deployed slides, and pax fled the aircraft, and are all over the airport, hopping the fence to seek help at neighbor’s homes, even venturing into town.  Hey, that family that US CBP was deporting, escorted onto the plane and stayed until we pushed back - has anyone seen them?
So diversion creates a Big Mess, and needless to say, the pilots do put some energy into avoiding it.  And that means time... tick tock, says the fire.

land a 300-pax jet at an airport with no Immigration facilities - been there, done that (as a passenger).  About 15 years ago, BA flight from Philadelphia to London, emergency landing in Goose Bay due to smoke in cockpit.  It was a 747 with about 320 pax (plus crew), of whom about half would normally need a visa to enter Canada.  Long story short - it was utter mayhem.

Second part of this answer could be distilled down to "capitalism costs lives". If a pilot feels something is wrong and they cannot control the situation, they should immediately divert to the closest airport, full stop. They should not have to worry about international politics or costs to the airline or the prospect of losing income or status if they made the wrong call. Yet that, unfortunately, is the case today - and that has cost, and will continue to cost, the most important and irreplaceable thing of all: lives.

@IanKemp Perhaps watch the miniseries Chernobyl before singling out capitalism for cheapness....

@Harper-ReinstateMonica This is gonna blow your mind, but criticism of capitalism does not imply endorsement of communism or any other socio-economic system. I know, amazing huh?

"When you look at fire-on-airplane tragedies, the pinch point has not been inability to make bare-minimum time to landing/evac. The problem has been pilots overestimating the time they have available."  In SR111's case, the investigation concluded that bare-minimum time to landing did exceed time available, even had the flightcrew immediately started an emergency descent.

It isn't practical for a number of reasons:

Intentional stalls are inherently dangerous. Stall-spin accidents are a major cause of accidents, stall recognition and recovery are taught specifically to avoid stalls.  Some airplanes have docile stall characteristics, but even those can still bite you. A Cessna 172 will drop a wing if mishandled, especially when heavy. Stall behavior at high altitude can be very severe
Some airplanes with a t-tail can enter what is known as a 'deep-stall', where turbulent airflow masks the tail and makes the elevator ineffective and the airplane unrecoverable
Situational awareness: dropping like a stone with the nose up does not give pilots a view of the outside, or see what mountain they may be heading towards
It takes time to do a controlled stall. You have to pull throttle and maintain altitude, degrading airspeed until you enter a fully developed stall. This isn't instant, in a light airplane it will take 30 seconds or so, I'm not sure how long it would be for an airliner at cruising altitude, but I imagine it may take a minute for a fully developed stall to develop and to get that high rate of descent, whereas you can be in a dive with a steep rate of descent in a much shorter time

Consider an emergency descent from FL400 (40 thousand feet) to FL100 (10 thousand feet) using the 2 methods: A dive at 8000fpm and a 'controlled' stall at 10000fpm, where it takes 30 seconds to get into a developed stall and high rate of descent:

60 seconds: the diving airplane is at FL320, the stalling airplane at FL350
2 minutes: the diving airplane is at FL240, the stalling airplane at FL250
3 minutes: the diving airplane is at FL160, the stalling airplane at FL150
3 minutes 30 seconds: the stalling airplane is at FL100
3 minutes 45 seconds: the diving airplane is at FL100

So, by these calculations the stall option saves 15 seconds to lose 30 thousand feet because of the time penalty to get into a stall in the first place. That's really not much, and considering the risks involved from the potential loss of control and spacial awareness it's simply not worth it.
Not only is it not practical, it's not necessary to descend faster. A high speed descent is required for a number of emergencies, a cabin depressurization being the most prominent one, but there you have emergency oxygen supplies which will last much longer than required, so a few seconds will make little difference to survival. With an in-flight fire or other emergency where landing quickly is imperative the limitation is not descent speed, but proximity to landing fields which determines survival.

Can you clarify what you mean by "A Cessna 172 will drop a wing [if] mishandled?" Are you referring to spin entry (I think so), or to structural failure?

Yes @TypeIA, I mean spin entry.

I like the answere, but is it fair to compare descent times for a given distance without comparing the end velocity? The stall would give a forward velocity which might allow for landing, while the dive ends up much higher speed, right?

I'd like to add the factor of passenger experience to this. I've never experienced a stall and certainly not in an airliner, but I would imagine that the experience somewhat resembles that of a rollercoaster more than a confident airliner approach and landing

Actually, it's not a rollercoaster @Erik. Typically there is a bit of a buffet, and then it feels...weird for lack of a better word. I won't say it's a non-event, but it won't compare to oxygen masks dropping or a fire on board.

@GdD that's very interesting. I would picture the falling sensation in your stomach and the airplane feeling like if its at a loss of control. I guess I have to experience it sometime to actually understand. Maybe it's hard to explain, but in your opinion how does it compare to the dropping sensation airliners sometimes put on you during flight? When it feels as if the plane dropped 5 meters

We sense acceleration, a 10,000 feet per minute dive won't feel much different from a 10,000 feet per minute stall once established in that rate of descent.

Normally, a stall and controlled flight are mutually exclusive.
That AF447 would descend as it did has to do with the relaxed static stability of the A330 and its rear cg location as well as the docile behavior of its airfoils with large separation on the upper side. In short: With some aircraft this is indeed possible and practical but with others it is highly dangerous.
This technique is even promoted by W. Langewiesche and called "mushing glide". To quote from my answer to that question: "I would only fly this after extensive stall testing at altitude, calm winds and when I know exactly how the airplane reacts to control inputs.".

Is W.L.'s mushing glide really a stalled descent? I always took him to mean a decent at some speed between stall speed and L/D max.

Thing is, if the airplane has a decent natural pre-stall buffet, it'll be unpleasant to do the maneuver. And if it has no buffet, you probably don't want to try it in the first place.

@nexus_2006: Depends where you want a "real" stall to begin. The descent is only steep if drag is high, which in turn requires a large separated area on the wing. This is definitely outside of the range of attached flow and well into a stall.

@PeterKämpf: Isn't it pretty much impossible for most aircraft to stay in a stall? Shouldn't a statically stable aircraft just drop the not and get out of the stall?

@Orbit: No, it's entirely possible, in extremis in a deep stall. Some people have this belief that a stall means a complete loss of lift. This is far from what really happens.

It is smarter to roll onto your side and maintain unstalled flight, executing a emergency spiral descent.  G loads on the wings are much lower as there is no need to maintain altitude, only to control airspeed.
With all due respect to our beloved Langewiesche, "mushing glide" technique is for much lower wing loaded gliders that are easily unstalled with a forward push on the stick.  The pilot is greatly aided by a stall warning buffet and is able to react in time.
To truly understand stalling a much higher wing loaded airliner, make a model out of lead.
Yes, it will fly at a high enough airspeed, but full stall recovery will take thousands of feet, and is there for an impractical technique. Jet airliners need to keep moving.

would high drag keep the plane from overspeeding?

Leaf - yes
Langwiesche's personal glider - yes
Lead model glider - no
400 ton airliner - NO
Finally, one needs to consider a rate of descent of 10,000 feet per minute is over 100 mph straight towards the ground.  The physics of bringing 400 tons to a halt (zero rate of descent) leads to the conclusion that 8000 feet per minute is adequate.

"The physics of bringing 400 tons to a halt (zero rate of descent) leads to..." a large hole in the ground. Not an ideal outcome.

100 mph = around 50 m/s = 2g load for 5 s, or 1.5 g for 10 s = 125 m or 250 m = 500 or 1000 feet. Why does that sound insane?

@Abdullah "Why does that sound insane?" Because if you your attempt to apply 2g doesn't go according to plan and you apply 10g instead the wings will fall off, or if the wings stay on but you decelerate too much, you will stall again.

@alephzero I may learn something: How do you get 10gs just like that?

Because you’re not in the habit of doing it, so you’re unfamiliar with the feel of the maneuver, and you make a mistake because of lack of experience or confidence.   That’s the same thing that’s been downing A320s and 737Max’s when they enter a flight condition they haven’t adequately trained. If you don’t stall your A320 every week for practice, don’t start doing it in the middle of an emergency.

@Abdullah for a very low wing loading it works fine.  On the other end of the spectrum, it's not just unstalling the wing, it's also pulling out of the dive.  Once a high wing loaded aircraft starts to accelerate downwards, it goes deeper into stall (AOA increases) unless the nose is brought down, which results in a dive. A very light plane pulls out in a few hundred feet, the heavier one cannot.

I was taught to dive and slip the airplane via pressure on the right rudder and left stick when I needed to lose altitude quickly. The slip soaks up energy and slows the airplane.  Visibility from the left seat is pretty good, flight is controlled, and it's not hard to resume coordinated flight from a slip. But this was in Cessnas quite a few years ago. Good practice may have changed for spam cans since then, and is almost certainly different for slat / flap / spoiler equipped airliners.

Yes - and practical enough it could save your life.
Spinning - which is a certain type of stall - was invariably fatal in the early days of flying, with 90% of fatal accidents attributed to this cause.
One of the first recoveries from a fully-developed spin was Lt Wilfred Parke RN in 1912 in an Avro G. It was written up for Flight magazine, and the manoeuvre became known as "Parke's Dive", a magazine article that became well remembered, as attested by J A Chamier during WW1 -

Maj J A Chamier who, while in France, found himself spinning as he
came from a cloud. While he was falling, he recalled an incident on
Salisbury Plain before the war when Lt W Parke RN had recovered from a
spin near the ground. When people had crowded round to congratulate Lt
Parke on his luck, he had explained that he had stopped spinning by
doing ‘everything wrong’. Maj Chamier likewise did the opposite of
what his experience as a pilot suggested and he also recovered. He
subsequently related his adventure to Royal Flying Corps
head-quarters. [Jones, H A The War in the Air, vol 7 (Ch VIII, 430/431)]

As R.F.C. pilots began returning from the Western Front to become flight instructors they brought with them experience in spin recovery. In the turmoil of air warfare, recovery procedures had been found by trial and error as a necessity for survival. Spinning commonly followed the disorientation that often occurred when pilots (without guidance from instruments) had to climb through cloud or enter cloud to escape interception, as in the experience of Maj Chamier above.
This experience was highly pragmatic: its benefits were both as a manoeuvre itself, and as a ruse to fool the attacker into believing their opponent had lost control. And so, according to multiple accounts, intentional spinning and its accompanying rapid descent became a deliberate, practical manoeuvre with uses in air combat.
 (Royal Flying Corps officer running a class on attacking manoeuvres aircraft can perform. source)
(Principal Source - B J Brinkworth On the Early History of Spinning and Spin Research in the UK Part 1: The period 1909 - 1929 Journal of aeronautical HIstory Paper No. 2014/03)

I think there might be a few differences between WW1 fighter craft and modern jet airliners, though.

Of course, but I thought the question was broad enough to warrant various perspectives.

The other answers all seem good, but I think are not complete. And Isay that with the utmost respect for the others who replied, most of whom are without doubt much more experienced pilots than me.
First point, and perhaps was mentioned, but when you are touching down, you do in fact intentionally stall the plane, or at least in small prop planes. I only have a license for them, so am not sure if it's the same for jets.
But in effect, there are two extremes of fixed wing plane. The first type has a high glide ratio: if you lose thrust, your lift is still quite close to weight. That's most prop planes. In fact, the upper limit of this is powered gliders, that don't actualluy need the thrust after take-off. The second has a very poor glide ratio, and as soon as you reduce thrust, you might not stall, but the lift is significantly reduced, and your vertical velocity becomes quite large. This is true for all jets: commercial and military.
In terms of the practicality of an intentional stall, if you are not intending to get lift anymore after it, or even turn, then there's not that much downside to it. How can there be if it's the standard procedure for touchdown in all fixed wing prop planes?
And in terms of killing your lift, without increasing horizontal or vertical velocity components, in a fixed wing aircraft, I don't see anything you could do that would be BETTER than intentionally stalling.
Except with a special plane like a crop duster, or STOL (Beaver etc), with huge flaps, that's not the case. Or with a plane where you can adjust your thrust, like with a Harrier, or Osprey.
In any case, the question is only about a LANDING (as in it doesn't specify the plane must take off again). I'm not sure what you were told, but my instructor told me any landing I could walk away from was not a failure, per se. So in some special case, maybe it's the best thing to do, to allow a walk-away?
And it doesn't say it needs to be with a commercial passenger jet either. I've not read all the replies, but I think they all assume too much, and don't think broadly enough. It is a thinking-out-of-the-box type question. Perhaps there could be specific circumstances where it makes sense.
As you all know, a fixed wing can stall at any speed, and any attitude, if you cause the airflow over enough of the lifting surfaces to stop creating lift. That's the definition of a stall, in any case. And a stall as it starts, could well be the best/fastest way to change your flight vector, if you are constrained in terms of time, engine thrust, or distance (horizontal and vertical).
If one assumes the plane was flying straight and level, not climbing, and at some height where it couldn't immediately touch down, then you'd need to specify or know the exact parameters about its flight condition to be able to answer this properly.
Obvously it's not the ideal procedure, because it usually leads to a loss of control with most conventional planes, but if one were to add more flaps on a current design, maybe it could indeed be of use.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What's IFR departure procedure from private field with encroaching obstacles but no published ODP?
So, this question's answer says that, absent a published ODP, I should be 35' above DER, and on a 200'/NM climb.
But the airfield in the town I grew up in, 26MA, has no ODP; but 200'/NM isn't even half of the climb angle you need to avoid the trees. (You'll be okay-ish on RWY24, but the trees blocking the way off RWY6 are twice as high. You need to get 65' up in 650' of ground, or more than 600'/NM.) Moreover, from experience growing up there, I know the whole town has mountains and trees everywhichway.
If I am going to fly IFR (because I have to wait until it's dark so the skydiving has stopped, for example), what should I be using as a stand-in for ODP?  Should I just assume the departure procedure is, "Don't hit those trees on your way out?" (Thus, >600FPNM, leaning heavily into the 'at least 200FPNM' language) But otherwise fly runway heading until 400' AGL? Then level off into 200FPNM, heading my discretion? I would assume this is a constraint on where they put the runway, since there's no other way for me to know what else might be lurking out there.
What's this going to sound like in my clearance from Boston Approach?

Night doesn't mean IFR, you can fly visually at night. But in the case of actual IFR without a procedure where there's obstacles around the departure procedure is don't.

@GdD I keep forgetting you can VFR at night.  So if I wanted to fly IFR, it's VCOA or no-go?

@757toga Okay, that's kind of what I was suspecting, then.  Does that basically preclude an IFR flight plan departing from Pepperell? If not, what's the first part of the route in my clearance going to sound like?

Seems critical to specify what class airspace is at the surface, and how high you can climb before getting into another class.  Yes, I know we can look it up, but it ought to be in the question.

And, btw, there have been at least a couple of past questions on ASE about flying IFR in class G airspace, and whether or not this requires some sort of clearance ahead of time for eventual entry into controlled airspace.

I'm being slightly sarcastic @WilliamWalkerIII, it's a matter of degrees. There's nothing stopping you from departing, the wisdom of doing so is what I would question. You may be able to make your own departure plan for obstacle avoidance with a reasonable margin of safety, but if you can't you're better off staying on the ground.

@StephenS the clearance (if issued) would be effective immediately, beginning at 0 AGL, and would not be contingent on the aircraft reaching controlled airspace. However, any directional instructions would have to be worded so as to apply only in controlled airspace, as mandated by 7110.65 4–3–2c1(c).

@randomhead By definition, no clearance can apply in uncontrolled airspace. But I did get the order of words wrong.

@Stephen, I definitely see your point, and the P/CG definition for "air traffic clearance" aligns with that. And yet: we "clear" aircraft to and from Class G airports every single day; see the .65 4–3–2b1. The pilot is 100% operating under Instrument Flight Rules beginning at an altitude of 0AGL when given such a clearance, and ATC is 100% providing procedural IFR separation ("blocking" the airport) for their departure or arrival.

You really need to question whether departing in IMC from an airport with lots of obstacles is a good idea. But it could be completely feasible: IMC doesn't mean zero visibility.
Let's say the bases are at 1500 AGL and visibility is unlimited, for example. 26MA is class G with E at 1200 AGL' and in daytime if you remain in class G then you only need to be clear of clouds. You couldn't enter class E without an IFR clearance, though, because VFR you need to be 500' below the clouds, and you only have 300'.
In that scenario you could file an IFR flight plan as usual. ATC will ask you if you're able to maintain terrain and obstruction clearance until you reach controlled airspace (class E) and/or whatever minimum altitude they can provide ATC services at.
See the ATC Orders 4-2-8(d):

When VFR aircraft operating below the minimum altitude for IFR
operations requests an IFR clearance and the pilot informs you, or you
are aware, that they are unable to climb in VFR conditions to the
minimum IFR altitude:

Before issuing a clearance, ask if the pilot is able to maintain terrain and obstruction clearance during a climb to the minimum IFR
altitude

[...]
EXAMPLE−
“November Eight Seven Six, are you able to provide your own terrain and obstruction clearance between your present altitude and six
thousand feet?”

Your exchange might go something like this:

N12345: Boston Approach, N12345
Appch: N12345, Boston Approach, go ahead
N12345: N12345 is on the ground at 26MA, request IFR to ORH [Worcester Regional]
Appch: N12345, are you able to provide your own terrain and obstruction clearance until reaching 3000?
N12345: Affirm, N12345
Appch: N12345 is cleared to ORH via own navigation, radar vectors, then as filed. On entering controlled airspace, climb and maintain 3000, squawk 3434, departure frequency 124.9. Clearance void if not off by 1330 Zulu, time now is 1320 Zulu.
N12345: [readback]
Appch: N12345, readback correct

Gotta love a departure procedure that implies "look at your life, look at your choices" as step  0. Thank you for this and the cite! That's the doc I didn't look at.

Downvote for gross misinterpretation of the .65. The section you quoted deals with the case where a VFR aircraft is already airborne and requests a pop-up IFR clearance (which could have been already filed, or not). A departure getting their IFR clearance off the ground would be dealt with per 4–3–2c1(c) and would sound nothing like what you quoted.

I gotta agree with @randomhead.

+1.  I think it would be more like "maintain VFR until ORH, you can expect your IFR clearance from there as requested..."

TL;DR: There are no instrument procedures into 26MA, so there are no instrument procedures out of it either. Proceed with extreme caution. Departure in non-VFR conditions is not recommended.

As @757toga mentioned in a comment, the FAA only conducts a "diverse departure assessment" at airports for which it has responsibility to design instrument procedures.

FAA JO 8260.46, 2–1–1a
(1) Where IFR departure procedures are authorized by the approving authority conduct a diverse departure assessment for those airports with approved instrument approach procedures. ODPs are developed by FAA Service Providers at locations where they have instrument procedure development responsibility.
(2) ODPs may also be required at private airports where the FAA does not have instrument procedure development responsibility. It is the responsibility of non-FAA Service Providers to ensure a terminal instrument procedures (TERPS) diverse departure obstacle assessment is accomplished and an ODP developed, where applicable.

ODPs and/or non-standard takeoff minimums are developed "when obstructions penetrate the 40:1 departure obstacle clearance surface (OCS) as described in Order 8260.3." From a brief look at Google Earth, you are definitely correct that this is an airport which would qualify; even setting aside the trees, there is a hill approximately 4750 feet from the departure end of Runway 24, for example, and that hill is 300 feet higher than the field elevation at 26MA. The FAA's standard takeoff minimums presume an obstacle rise of no more than 152 feet per nautical mile from the runway; this hill is 2.5 times higher than that!
However, if neither an FAA Service Provider nor a non-FAA Service Provider has developed an instrument approach procedure for 26MA, then no one has conducted that diverse departure assessment and created non-standard takeoff minimums. This means there is nothing you can rely on but your own knowledge of the area when deciding whether to depart from such an airport under Instrument Flight Rules and in Instrument Meteorological Conditions.
It is not ATC's responsibility to know this information nor to police your activities, which is a common theme throughout JO 7110.65. ATC clearances are predicated on known and observed traffic; the pilot-in-command is presumed to have all appropriate certifications and currencies, to be flying a properly certificated and airworthy aircraft, to be operating in compliance with the applicable FARs, etc, etc. Even if an ODP does exist at an airport, ATC will not assign it unless it is necessary to ensure separation (JO 7110.65 4–3–2c2), and unless it is assigned "compliance with such a procedure is the pilot's prerogative."

So the clearance you would receive from Boston Approach would be the same as the clearance you would receive when departing any other Class G airport, whether public or private, and would—in accordance with 4–3–2c1(c)—sound something like this:

November 12345, cleared to [destination] airport as filed. Maintain three thousand, expect five thousand one-zero minutes after departure. Departure frequency 124.9, squawk 1111. [If necessary: When entering controlled airspace, fly heading 260.] Hold for release.

But this is assuming you would be issued a clearance off-the-ground at all. Note how close 26MA is to ASH, and to the ASH Class D surface area, and note how (according to the Skyvector link you posted) the airport has been analyzed to be "NOT OBJECTIONABLE IN ACCORDANCE WITH VFR." I don't want to say it would be impossible for you to get an IFR clearance while still on the ground at 26MA; nothing is impossible. But I could easily imagine it being unlikely.
For completeness: If you did take off from 26MA and attempted to pick up your IFR clearance airborne, you would need to either be at-or-above the minimum vectoring altitude when receiving the clearance, or you would need to confirm—per 4–2–8d—that you are able to "maintain your own terrain and obstruction clearance" until reaching the MVA, even if you may go IMC before that altitude. Obviously this is something that you should only agree to if you are very confident of your location and the location of any nearby terrain and obstructions, and the performance capabilities of your aircraft. It would not be the recommended Plan A.
The difference between getting your IFR clearance while you are on the ground at an airport and getting it after you have departed is, of course, the assumption that the area around the airport has been analyzed and an ODP or non-standard takeoff minimums have been published. That assumption does not hold true in this case, but the 7110.65 does not take account for that.

CONCLUSION: Although I do not believe this is a requirement per 14 CFR Part 91, the smartest thing would be to apply the "can I file IFR to this airport" rule in reverse. Namely, as you alluded to, the safe move would be to only attempt a departure from 26MA—or any airport which does not have a published instrument approach procedure—if the ceilings are no lower than the local Minimum Vectoring Altitude, meaning you can climb visually to that safe altitude. ATC procedures do not make distinctions between airports that are and are not served by instrument procedures and you cannot rely on ATC to provide a sanity check in this situation.

I tried to ask the airport operator. But the airport manager's email bounces. Sooooooo...

@757 I wonder that myself, to be honest. And yet it is listed as approved phraseology in Chapter 4.

@757, edited to address your last point. Let us continue this discussion in chat.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Oil Cooler Bypass
I am wondering here, in relation to a oil cooler bypass. I know that we have a gauge to detect the oil temperature and make the oil bypass the cooler completely if it gets too cold. My question is, if that gauge malfunctions and stop doing its job, does the oil have another bypass at the cooler to stop the viscosity to become too high? Or would it eventually clog there without a way to bypass it?
Or am I completely wrong in this one entirely?

Any answer about the operation of systems to bypass oil coolers will depend on the airplane you are asking about, but it seems that you are worrying about something that just isn't a problem.
It is unlikely that any oil cooler could be so efficient as to cool the oil into a thick sludge that stops circulating.  It just isn't that thick to begin with, and the engine provides plenty of heat so you probably want the default mode to be through the oil cooler.

That is a fair point. Following that line of thought, I also do belive the bypass would be implemented based on pressure instead of temperature itself. I was wondering because I have learned that there are certain coolers that would check the oil temperature to decide if they should divert the oil instead of allowing it to continuously passing through the cooler getting more and more cold. But I also understand your statement. Would have to be a hell of a descent and prolonged time to allow oil to reach that state, maybe.
I do tend to overthink things. Thank you for your answer!


text:
Fabric-covered Clark Y Max Coefficient of Lift
I'm looking at the Aeronca C-3 Collegian, which had a Clark Y airfoil, and I'm finding the following:

Wing area: 142 ft²
Empty weight: 466 lbs
Payload: 470 lbs
Stall speed: 38 mph

When I do the math for that wing area, a gross weight of 936 lbs, and a stall speed of 38 mph, I get a coefficient of lift of of about 1.8; that's higher than I see from either simulations or wind tunnel tests.
I'm inclined to trust these figures, since they line up with pilot reports on the C-3, and the airspeed range would be very narrow if the stall speed were higher; could it be that distortion of the fabric results in a later stall?  The little I could find on the subject doesn't suggest any such effect.  What's going on here?

One contributor with a lightweight airplane like the C-3 is thrust.  At a high angle of attack, a significant fraction of the engine's thrust is directed downward, lightening the loading that the wing's lift is working against.  Even at idle, this allows slowing further before the angle of attack becomes critical -- making the coefficient of lift appear higher than it is.

That's not a bad thought.  If I say 250lbs thrust total, which seems reasonable for a 35 hp engine, the vertical component at 18° angle of attack is about 80 pounds, which reduces the Cl needed to about 1.6, which fits the data I know better.

Sometimes the stall speed listed is the indicated airspeed at stall, where there can be significant calibration error and the A/S will read 3-5 mph low.  If it doesn't say 38 mph CAS (calibrated airspeed) you can't really be sure if it's corrected or not.

Keep in mind that the stall speed is not always given for the max takeoff weight. The official aircraft manual (if exists) lists effects of takeoff weight on stall speed.


text:
What is the purpose of a walled area in the vicinity of Heathrow Airport?
Looking at a satellite map to the East of Heathrow Airport, there is a small passenger jet parked in a walled off area. Looking at the aerodrome chart the entire area is listed as Bealine Base, which I assume is used for BA operations. What it the purpose of this walled off area?

Possible duplicate of What are the steep ramps often erected at large airports?

There is a similar wall on the corner of Dallas Love Field as seen in this google street view.  This wall may actually be a part of some maintenance operation rather than the airport itself, but it's the same principle.

The suggested-as-duplicated is not the same thing. This is an engine run facility, with 3 walls to contain not just jet blast but also noise. What's in the not-really-a-duplicate question is just a wall to protect an area from jet blast. These engine run facilities have far more structure than the jet-blast barriers.

If we told you we'd have to kill you.

This is a time-out corner for planes which experienced minor incidents on their last flight.

Here is an example engine test run at full thrust that takes place in this kind of walled off area: https://www.youtube.com/watch?v=lAJNoJvpftY

It seems that another question does actually provide the answer to this, but in that case the question is asking about a ground run up area that is formed from a loop of taxiway: https://aviation.stackexchange.com/questions/52663/what-is-the-purpose-of-this-loop-in-a-taxiway

say @Jan thanks for that video - but if it's so dangerous why was there a hand-held camera right there ??  :O

That's where they reload the airplanes with chemtrails stuff.

@Fattie it't not so much about being dangerous, it acts more as a sound barrier and to redirect the jet blast away from the airplane or any nearby structures or vehicles

a few people gave mentioned the sound aspect, @Jan - you know, I really doubt they "stop the sound" much.  Although it might help a bit, sound trivially travels OVER barriers (all that "wave" crap they taught us about in physics, recall! :)  )   I honestly doubt that the primary reason is sound reduction.  I bet the actual reason is indeed safety (stop stuff being thrown around, etc) and any sound reduction is just a bonus.  Anyways.

Damn - that being said, the link in the answer below specifically shows it as a product primarily focussing on the acoustic aspect!  Heh !   :)  Sometimes, you're wrong ...

@Fattie, haha yeah I was about to say that, if you look at the link to the IAC website from the answer below they advertise the facility's noise reduction capabilities.

I left my TOTALLY WRONG comment there, as sometimes you have to man-up to having been TOTALLY WRONG.   (Naturally, usually when I am totally wrong I just delete the post  :-)  )

It allows them to do a run-up test of the engines without blowing debris at other parked aircraft, people, or things on the ground.
[Credit to Ralph J]
The walls have a structure that allows the noise of engine run-ups to be absorbed as well. Engine run-ups, especially multi-engine run ups, can be very loud.
You can read more about IAC-Acoustics ground run-up enclosures here.

The walls also are constructed to absorb the considerable noise that a high-power engine run generates - which is part of the reason that these structures have 3 sides rather than simply 1 wall.

These are IAC acoustics ground run enclosures; as the name and Ralph J suggest, the primary purpose of their shape is noise reduction.

If the primary reason for the walls is noise then this answer needs to be modified or another answer given.

I'll add the extra info from Ralph when I get back to my computer.

Interestingly, the linked IAC-Acoustics page includes a video with the same run-up enclusure at Heathrow shown in the question - unless there were more than one in that airport. https://www.youtube.com/watch?v=MRbAaAInMH4

These structures are super important. My father told me of an incident in Hellinikon airport, where an Olympic Jumbo did a run-up test of the engines, and some policemen that were curious came relatively close (to an agnostic person, they were still far away); the police car rolled over from the blast, killing both guys that day.


text:
How do I figure out the right pronunciation for transitions?
For example, the CNERY transition,* how exactly is this pronounced? On the VATSIM community, it seems there's a huge debate on what this is called. Some people say CONNERY, and some people say SCENERY. I personally say SCENERY since it makes more sense, but what is the most proper one? And is there a place where we can find pronunciation of such things?
Like another one is SCTRR transition which some people say SCOOTER, some people say SCATTER.
* CNERY transition is part of KLAX's DOTSS TWO DEPARTURE.

Welcome to aviation.SE! You mentioned that you've heard the real-world pronunciation, so I'm not sure what additional information you're asking for. Are you looking for some sort of pronunciation guide for waypoint names? And the [tour] may be helpful if you're new to StackExchange.

I think @IAmNoobPilot is asking for the correct one, maybe doesn't know that both are correct and used?

@Jihyun Oh both is correct? thank you!

I've only taken classes at uni so far, but for my pilot and leadership studies in rotc whenever case studies with such terms come up as long as it's widely accepted, understandable, and sensible they are usable. this is only on my personal experience, that's why i framed my earlier comment as a question because there are far more knowledgeable people who will know this for sure ;)

For SCTRR, the pronunciation that came to mind for me wasn't SCOOTER or SCATTER, but SCUDDER.

It would be nice if there were an authoritative, canonical, source for these sorts of waypoints, but sadly, I don't think one exists. I say that because I hear controllers sometimes using a different set of vowels or syllable emphasis "today" than they did "yesterday". If there were a single "right" way to verbalize CNERY or SCTRR, I'd expect ATC to have them all down. But in plenty of cases beyond those two, it remains unclear.
For example, the JFRYE arrival into Dallas -- is it the "Jeffrey" or the "J-Fry" arrival? You hear both from Ft Worth Center all the time.
My conclusion: no cannonical source exists.

Page 9 of this FAA handbook includes pronunciations for the Cleveland/Detroit Metroplex:

Interesting, do they publish these for other areas?

Nice find - thanks for posting that!

There is no single "correct" pronunciation for fix/waypoint names. The only rule is that the pronunciations must be unambiguous with respect to all other nearby names. For CNERY, jf one controller says "Scenery" and another says "Connery", and neither is ambiguous, then both are arguably correct. Heck, I'd even accept "Canary"; maybe the local fixes are named after birds but CNARY was already in use elsewhere.
As a practical matter, pilots should read things back the same way the controller said them. The point of communication is to be understood, so as long as that's happening, the details aren't important.

No canonical source exists because the regs do not require one, the local ARTCC facility is actually responsible for making sure there are no "similar sounding fixes" which is why there may be local pronunciation lists but as per the regs:

Five-letter names that are assigned by the Mission Support, Terminal
Procedures and Charting Group and major commands will be coordinated
with the associated ARTCC to preclude similar sounding fix names.

You can find the full order on how fixes are named here which tells us that they merely must be pronounceable:

A single five−letter pronounceable combination serves as the fix name,
assigned identifier and computer code. If a new fix is to be
collocated with an existing navigation aid, ILS marker, way point, or
other type fix, the original name or name−code applies to both.

So the fix names must be unique according to the local facility and subsequently the local pronunciation.
Some notes on what I have actually experienced flying:

If the fix name seems ambiguous to pronounce the controller will spell it
Controllers generally dont mind if you confirm one by spelling it
If you mis-heard a fix and type it into foreflight while getting you IFR read back its usually 1000 miles off course and obviously wrong (thats why there is a 300NM radius for names)
If you fly near Philly enough you are bound to get assigned Piper XXXXX decent to tree thousand cleared into the bravo and no matter who much wiz wit' you get when you land there is no number tree

In line with the above note about hearing it wrong, this is why pre-flight chart perusing is key, and why pop up clearances can be tricky. On a recent IFR flight from VA to CT I had a mid route clearance change near Allentown due to weather and traffic, the controller spelled at least half of the fixes over the radio for me...

According to the FAA (which I believe follows ICAO exactly?), numbers are pronounced as follows: wun, too, tree, fow-er, fife, six, seven, ait, niner. But in the USA only "niner" is used with regularity, in my experience.

@randomhead indeed niner is proper radio telephony

...as are "tree" and "fife," according to the 7110.65 table 2–4–1. But hardly anyone actually says that in the US.


text:
ILS Approach, when can you descend on the glide path?
The following quote is from G. Bristol’s book, Ace the Technical Piloting Interview:

You can descend on the glide path when

You have been cleared for the ILS procedure.
You have captured the localizer, within ±5°C. [sic]

Regarding point 2. There is plenty of discussion about what it means to capture the localiser and/or be established on the localiser (e.g. see airliners.net discussion).
Can someone please clarify, from an ICAO PANS-OPS perspective, the point that a pilot can descend on a glide path on an ILS approach with regards to the localiser, following a clearance for the ILS (and EASA & FAA differences to ICAO).
Regarding point 1. Would the word approach would be better than procedure? For example, an ILS published procedure approach might involve an IAF, perhaps an outbound leg to a platform before the start of the glideslope descent. Whereas you can be cleared for an ILS approach following radar vectoring at a altitude above the published platform altitude.
Thank you.

I would suggest that these two questions are dissimilar enough that you should edit this one to focus on one only, and ask a new question for the other one. FWIW I agree with your interpretation of Point 1.

Does the above assume that everything on a procedure plate must be followed? Why does clearance for the procedure imply that it is necessary to fly over the IAF? On a VOR/DME approach with two arcs and a Procedure Turn depicted, it is obviously not necessary when given clearance for the procedure to specify which arc or PT you are flying, if any.

You’re making this more complicated than it needs to be.
Once you are cleared for an approach and established on any segment of that approach, then you may descend to the altitude published for that segment.  If the segment has a glide slope/path rather than a fixed altitude, you may follow it down.
That raises the question of exactly when you are “established”.  The obstacle clearance surface extends out 50% wider than full-scale deflection. However, since the HSI needle pegs at full scale, you must be less than full-scale deflection (i.e. off the peg) to be certain you are within the protected area.
A localizer beam is 5° wide, so full-scale deflection is a mere 2.5° off course.  I suspect the quoted author meant (less than) full-scale deflection but forgot to halve the width.


text:
Is APU bleed air blow back a genuine risk on the 737?
On a warm day, having the APU1 bleed on provides pressurised air for the air conditioning packs to operate, cooling the cabin. During engine start, this bleed air is redirected to the engine starter valve to initiate the main engines. (Frequent flyers might notice passengers reaching for the nozzles, not realising the air is now used for engine start.) After the engines start, they supply bleed air for air conditioning, allowing the APU bleed air to be switched off.
My question concerns taxiing back to the stand after a flight. The APU is typically started during this time preemptively, as it will be needed to supply electrics on stand, bridging the gap until ground power is connected. The APU provides power during this transition, which frequent flyers might notice as a brief flicker of the lights – the switch from engine power to APU power.
On warmer days (but not necessarily markedly "Hot Weather" days2), there's also a need to transition from engines supplying bleed air for air conditioning to the APU doing so.
On the 737, the bleed air duct is shared by engine number 1 and the APU. If too much air pressure from engine 1 hits the line, it might cause "blow back" into the APU if the APU BLEED switch is on.
In my company, we avoid turning the APU bleed air switch ON until both engines are below 20% N2 to prevent this "blow back." However, this procedure is not referenced in our SOPs, and to my knowledge, it isn't mentioned in the 737-800 AFM, FCOM, FCTM, or QRH.
So, is this danger of "blow back" a genuine risk to the APU bleed system operation, or is it a practice that has been informally passed down among pilots without substantial evidence?

1 An APU (Auxiliary Power Unit) is a small engine which sits in the rear of the 737-800 which can provide electrical power and compressed air for cabin air conditioning and engine starting. This is typically a Allied Signal 131-9(B) for the Boeing 737-NG
2  The “Hot Weather Operations” (Outside Air Temp above 40oC/104oF) supplementary checklist refers to turning the engine bleed air switches OFF before turning the APU switches ON. (The APU does a better job of providing bleed air in this scenario compared other the engine).

So, is this danger of "blow back" a genuine risk to the APU bleed system operation, or is it a practice that has been informally passed down among pilots without substantial evidence?

There are two related paragraphs in the Boeing FCOM, and one in the AFM.
Boeing FAA-approved AFM (D631A001 revision 31, 2011)

Except for engine start do not open APU bleed air valve when LH
engine bleed air valve is open, or when isolation and RH engine
bleed air valves are open.

Boeing FCOM (D6-27370 revision 26, 2010)
AFM operational (see a copy here):

The DUAL BLEED light illuminates whenever the APU bleed air valve is open and the position of the engine bleed air switches and isolation valve would permit possible backpressure of the APU. Therefore, thrust must be limited to idle with the DUAL BLEED light illuminated.

Non–AFM operational information (see a copy here):

APU bleed valve may be open during engine start, but avoid engine power above idle.

Note there is also a possibility of backpressure of the engines 9th stage by the APU at idle thrust, causing the engine valve to close:

With both the APU and engine bleed air valves open, and the engines operating at idle thrust, there is a possibility of APU bleed air backpressuring the 9th stage modulating and shutoff valve. This would cause the 9th stage valve to close.


text:
Does the yaw damper require manual activation on modern airliners?
Modern commercial aircraft are equipped with yaw dampers. This post explains the feature. Now I was wondering if there is a button to manually activate and deactivate it (e.g., on a Boeing 787) or if the yaw damper is automatically activated when the autopilot is engaged?

As I remember, on 747-100/200 aircraft the yaw damper is always on, the only way to turn it off being to pull a circuit breaker. Normal operation of the airplane is to take your feet off the rudder pedals as soon as you have lifted off and not put them back on until just before you go into the flare for landing.


text:
Which clearances are issued by ATC without the pilot requesting them?
Some clearances are only provided after specifically requesting them, such as the departure, engine-start, taxi or oceanic crossing clearance. Line-up and Take-off clearances are issued once the pilot relays to be ready for it (this could be viewed as "actively requesting" the clearances.
As I have learned after this question, sometimes descent clearances are issued by ATC without the pilot asking for it. Which other clearances are issued "automatically"? Specifically, I'm asking about the approach clearance and the landing clearance.

I receive clearances into class B without requesting them.  Usually a controller being nice and eliminating a shelf as an obstacle to a climb.  I'll also receive clearances for "the option" when doing touch and gos without a request.

No clearance is issued without the pilot requesting it. But a request is not just something you do on the radio. The interesting questions here is: how do pilots request something?
The most common way is through a flight plan. By filing a flight plan, the pilot details the planned flight, from departure to destination, via a predefined route, with a requested speed and level. ATC will issue a flightplan clearance prior to departure or prior to entering controlled airspace. This covers the general flight, and basically lets the flight take place.
During the flight, specific details need to be requested by the pilot - such as taxi - but only if the controller is not already aware that the flight is ready for whatever it is they are requesting. For example, during radar vectors for approach, ATC already knows that the flight is requesting approach at their destination (since the destination is noted in the flightplan), so ATC will clear the flight for approach without needing the pilot to explicitally request it. Same goes for landing clearance. The pilot does not have to explicitally say "request to land", because this is already a part of the flight plan. ATC will automatically issue a landing clearance when appropriate.
ATC can issue instructions or clearances to flights that deviate from their flightplan if needed for safety or efficiency reasons. For example, ATC may instruct a flight to change level due to traffic ahead on the same level. But the flight plan is always the basis for all clearances.

good explanation, thank you!

As I commented on the question, ATC often gives me takeoff or route clearance without any request. Is this a difference of rules.

@JonathanWalters Your request is you submitting a flight plan. By submitting your flightplan, you request to fly in accordance with that flightplan, so you do not have to detail your request on the radio

OK, and I suppose by the same logic, my taxi request to ground is sufficient initiation for Tower to issue my takeoff clearance even though I may not have contacted them?

@JonathanWalters Exactly. Essentially, they already know who you are and what you want, so you don't have to tell them

ATC "clearance" is only used in specific situations:

A route clearance - pilots request this when ready
Takeoff clearance - pilots assumed to be ready unless they say otherwise
Approach clearance - ATC provides this once the aircraft is positioned
Landing clearance - ATC provides this when ready

All of these are very important details of the flight, and avoiding using the word "clearance" in other situations prevents confusion about what ATC has cleared the pilots to do. (There are others but for the typical commercial flight these are the main ones)
Anything else would be an instruction from ATC. Pilots may make requests but are expected to follow these instructions unless they feel that it would compromise safety.

Before the flight, the pilot will request their route clearance. ATC will respond by clearing them to fly to their destination via a certain route. This is usually the only clearance pilots receive before takeoff.
The pushback will be requested by the pilot. At large airports ATC may coordinate gate operations but this is not technically a clearance, but an instruction of when and where to push. The ground crew may let the pilot know when they can start their engines, but again this would be an instruction.
Taxi will be requested by the pilot, but again ATC will give them instructions, not a clearance. When crossing an active runway, ATC will give an explicit instruction to either cross or hold short of the runway. This is not a clearance but pilots should repeat these instructions back to ATC to help prevent runway incursions.
Upon reaching the runway, especially at a busy airport, the pilots are assumed to be ready. If not they must inform ATC. ATC will then give the pilots their clearance for takeoff. At a less busy airport ATC may wait for the pilots to request clearance. Depending on traffic, ATC may give a "line up and wait" instruction. Then the pilots will be cleared for takeoff.
Once in the air the pilots are expected to fly the route that they were cleared for. Depending on conditions, pilots may request or ATC may offer certain shortcuts or deviations from their route. This could be just a temporary vector. ATC may also clear them to a certain navigation point, but this changes their clearance limit. They are no longer cleared for the rest of the route, only up to where this amended clearance ends. ATC must provide further instructions, which could be as simple as "and then on course".
Changing altitudes are instructions from ATC. ATC will instruct the pilots to climb to the altitude indicated on their flight plan, depending on conditions. Pilots may request altitude changes for weather or performance reasons. Once nearing top of descent, pilots can request descent if ATC hasn't allowed it yet.
Arrival procedures will often require ATC instructions to get the pilots lined up with a runway. ATC will provide them vectors and altitudes. ATC will then clear the pilots to fly an approach to a certain runway. Although pilots may request a certain approach procedure, ATC will decide when to provide the clearance.
Once the aircraft gets closer to the runway, ATC will give clearance to land. The pilots shouldn't have to ask unless they are unsure of their clearance or the tower seems to forget it. If the pilots aren't cleared to land by a certain point, they must follow any missed approach instructions that are given in the approach procedure they were cleared for or by ATC.
Once on the ground, the pilots will receive instructions for taxiing to the gate.

Taxi instructions are not a clearance with one exception, according to the AIM 4−3−18. Taxiing 4. 5. A clearance must be obtained prior to crossing any runway. ATC will issue an explicit clearance for all runway crossings.

@JScarry The AIM calls it a clearance but it's more of a special instruction, I'll edit to try to clarify that bit.

An ATC clearance is needed to enter Class B Airspace

@SteveKuo yes, that's one of the additional clearance I left out, airliners are typically on IFR plans in contact with ATC and so don't need an explicit clearance.

This question and this forum is not specific to airliners/IFR


text:
Were there any planes used in WWII that were able to shoot their own tail?
In Indiana Jones and the Last Crusade, there's a scene where Indiana is piloting a plane and his father is acting as gunner. While shooting at incoming enemy planes, he accidentally shoots his own tail, forcing an emergency landing. According to an Indiana Jones Fandom page, the plane represents a German D-EKVY, although for the film they used a Stampe SV.4 biplane.
Were there planes used in actual combat during WW2 able to shoot their own tail as depicted in the movie?
Front guns were usually equipped with a synchronization gear to prevent pilots shooting their own propeller when engaging enemy planes. Was there a similar device to prevent planes from shooting their own tail?

Duplicate: https://aviation.stackexchange.com/questions/55402/can-the-dome-gunner-on-a-b-17-flying-fortress-shoot-the-planes-tail-off

Definitely highly related, but that question was about one specific plane--

Bombers with power turrets incorporated profile cams that disabled the firing mechanism when the gun barrel swept a part of the plane. In the case of a pintle mounted flexible machine gun however, nothing to stop you shooting the structure.

The Douglas SBD Dauntless's rear gunner could shoot its own tail.
The SBD-5 had two 30-cal machine guns that could be popped out of storage in the aft fuselage and locked into a ring frame around the gunner's seat.  That seat can rotate and pivot in several directions.  The gun is mounted on a ball joint that allows it to rotate freely.
There is no mechanism or stop to prevent the gunner from shooting off the vertical tail.  It might have been impossible to shoot off the horizontal tail, but I don't quite recall.
I used to volunteer for an organization that restored, maintained, and flew an SBD-5 as a flying museum.  I've spent several hours in the back seat on pleasure flights, cross countries to airshows, and flying in airshows and photo flights.  This is me in the back seat.

One year, we hosted a reunion for a SBD squadron.  Seeing those old timers interact with their airplane again was amazing.  I remember one 80+ year old who hobbled with a cane.  His face lit up when we said he could touch the airplane and even more so when we said he could get in.  We prepared to help/lift this guy into the back seat when he dropped his cane and with one swift motion was up the side and into the back seat.  Before you know it, he had the seat turned around and the guns drawn.  It was all one fluid motion of 60+ year old muscle memory.  It was beautiful and heartwarming.
A woman asked him "What kept you from shooting the tail off?".  He gave the deadpan response "Fear of dying."

What an absolutely awesome response from the veteran!

This is why you need cameras rolling all the time on valuable artefacts where the public has access, to catch vandalism, thefts, and acrobatic octogenarians with machine guns.

Your SBD seems to have a line painted onto the vertical fin indicating how much can be safely shot off.


text:
Why are wings not tapered all the way to reduce vortex drag?
Wingtip vortices are created by, well, wingtips. These vortices create drag. One of the approaches to reducing this drag is taper the wing,

source

source
Will eliminating the wingtip, as on the lower left, eliminate these vortices, and thus eliminate induced drag? Why or why not?

What did this question get a downvote for.........?

@Abdullah I would guess the fact that it is not really clear.

This question doesn't make sense to me. Taper from where? 'All the way' from what? You can't prevent a wing stall.

Do you mean taper to a point so that the tip chord is zero?  Could be stated a bit more clearly--

I think the fact the OP is called idonotknowmuchaboutaviation means that we should cut them some slack

all the way from the ending portion of the wings.

yes, I mean taper to a point so that the tip chord is zero or near zero but the taper is not uniform. the taper increases a lot at the ending portions of the wings. kind of like a elipse wing.

Post a picture of a wing "ending portion" and then sketch onto it (MS Paint or similar is just fine) a rough approximation of what you're thinking. As they say, a picture is worth 1000 words, and, at the moment, your words are failing to accurately convey to others what you're thinking. (Doesn't mean you're thinking wrong, just that you're not explaining yourself well enough.)

@DaveGremlin we don't have a problem with not knowing, or we would not be here, but we need to understand what the question is about to answer it. and if it is not clear we can't answer it, that's why comments and the edit functionality exist. if the question is ambiguous, there is no slack to cut.

@Federico sorry just edited the post but still I guess it looks crappy

@idonotknowmuchaboutaviationa the "crappyness" is not a problem, but it would help if you could highlight (maybe with another color) what you want to look at specifically.

Pretty sure he is asking about the difference between a straight "Hershey bar" wing, and one shaped more like a Spitfire, that ends in a point.  Why are we not getting that?

@MichaelHall Possible, but I doubt that. If you're right, then of course, the answer would be "It has been done, it reduced vortex drag, but we don't like doing that because it's too hard to build wings that rounded"

@Abdullah, well the person asking the question is mixing up wing stall, tip stall, and vortices, but from the title question alone it should be clear that he/she is fishing for pros and cons of a wing tapering to a point versus one that has a "clipped" end.  I have seen more poorly worded questions decoded adequately by experts who state any presumptions and clarify the question in the answer.

Does this answer your question? How does an aircraft form wake turbulence?

I believe https://aviation.stackexchange.com/questions/8877/ explains all that needs to be explained already.

@Abdullah that is not exactly what I am asking. I think the wing on the lower left would be prone to tip stall because of the high taper. what I want to know is why can't the wing have moderate taper and the ending portion of the wings be like that of elliptical wing or pointed tip wing? from what I understand complete elliptical wings are not formed in large numbers because they are difficult to manufacture. doing what I am saying should solve the problem of cost right?

@idonotknowmuchaboutaviationa a trapezoid with a circular tip? In that case, the answer is definitely yes, it does reduce induced drag, probably a liiiiiiittle less than the ellipse. As for manufacturing, I cannot say, though it probably would be easier.

@Abdullah then why are planes not made that way. if commercial airliners were made that way the size of the wingtips can be reduced or there need can be completely eliminated which would decrease drag.

One of the approaches to reducing this drag is taper the wing

No, not at all. The vortex strength depends on the lift at the center wing. This strength invariably tapers to zero towards the wingtip, regardless of the wing's geometric taper ratio. The taper ratio will only change the local gradient, not the absolute decline in vortex strength. In the end, what happens at the tip is insignificant for the shape and strength of the wake.

Skybrary claims, without explanation, that taper weakens tip vortices (penultimate paragraph).  Maybe that says more about Skybrary than about aerodynamics.

@CamilleGoudeseune Nonsense like this gem: "Although there must always be at least some induced drag because wings have a finite thickness …" confirms your verdict. More nonsense: "Well designed winglets can prevent about 20% of the airflow spillage at the tip - and therefore 20% of the induced drag." Whoever wrote this had no clue.

I suppose one can argue that the tip vortex is just a component of the overall trailing vortex; a tip can exert downforce with its local vortex reversed, but it makes no difference to the overall picture. Winglets do reduce tip vortex strength and they do reduce induced drag, so any kind of blanket statement/denial is dangerous.

@GuyInchbald sorry I didn't understand what you are saying.

The relation between tip vortex strength and induced drag is not a simple one and the suggested advantage is not realised in practice. Meanwhile, a pointed tip has other problems. Some that occur to me:
If the wing has a constant aerofoil profile then a pointed tip will tend to stall first at high angles of attack. This creates turbulence over the ailerons and reduces pilot control at a critical moment. Changing the aerofoil such as twisting downward or "washout" reduces the problem. For example the de Havilland DH.88 Comet racer of 1934 has a fairly pointed wing with no washout - and a notoriously vicious wing-drop in the stall. American replica N88XD has around 2 or 3 degrees (I forget exactly) of washout to try and ease this, with the same being included in the restoration of Comet G-ACSP Black Magic.
But reprofiling the outer section changes the lift distribution to a less efficient one. Widening the tip section can help restore efficiency, as well as further reducing the stall problem.
Structurally, a fine point is both prone to damage and difficult to fit a robust aileron hinge inside. The ailerons have to be moved inboard to a wider part of the wing, which reduces their effectiveness.
The point contributes little lift but significant moment and physical width, so removing it improves aileron and gust responses and eases ground handling, without any significant lift penalty.

someone had edited my question. I want to know is why can't the wing have a moderate taper and the ending portion of the wings be like that of elliptical wing or pointed tip wing? from what I understand complete elliptical wings are not formed in large numbers because they are difficult to manufacture. doing what I am saying would reduce the possibility of tip stall, won't it?

I see what you mean. Wing tips are often rounded, rather than cut off square. But cutting at angles with a stubbier pointed tip, as in your original drawing, still has several of the problems of the pointed tip that I mentioned. Does that help?


text:
How does control system design ensure correct elevator position with the steering system unlocked?
I’m having some trouble answering the following problem encountered in one of the worksheets for aviation students:

The plane shown in the picture stands on the runway. The pilot, while getting off, did not lock the steering control system. Nevertheless, the elevator remained horizontal. How can this effect be ensured in a correctly designed control system?

I'm looking forward to some hints. Thank you in advance

Two downvotes, three close votes, and zero constructive criticism?!  OK, I'll start:  The pilot "getting off" has a different meaning for most native English speakers, but I will assume you meant securing and leaving the airplane parked after a flight?  That makes some sense from the context of the control locks, but then it wouldn't be on the runway.  Did you mean taking off? Please clarify.  Other than that, there's probably an easy answer for the control surfaces being neutral when stationary that has to do with springs and counterweights, but I don't have the engineering chops to answer...

@EngineerinProgress sorry the tomatoes are flying on this one.  In the future it may be best to reference your source as foundation.  Who published this "worksheet for aviation students", or is it for engineering students?.  Yes, a hanging heavy solid steel control stick might help hold the elevator level, but at rest, with no one in the plane, the elevator is best pointed down a bit so a gust doesn't fly the plane off the ground.  In flight, the trim tab holds the elevator in place through aerodynamic forces.  It is generally not a good idea to hop out of a plane without securing it.

This is a somewhat dumb question, but here's one take at an answer.
The upside-down control stick with the rigging shown tries to remain vertical by gravity. If a wind gust tries to push the tail down, the fuselage will rotate clockwise and the control stick will then apply a nose-up control force to the elevator and make the nose-up pitching moment worse.
To prevent this, the upside-down control stick has to be rigged in the opposite sense so a clockwise (pitch up) motion of the fuselage will cause the stick to apply a pitch-down control force to the elevator.

Totally agree with your assessment of the homework question. Who says that a "correctly designed control system" means the elevator is aligned with the horizontal stab when there is neither aerodynamic force nor pressure on the controls???

It seems that this question is about how best to design an aircraft control system so that the elevator remains horizontal when the aircraft is at rest on the ground with no one in the cockpit and no control locks installed. It seems likely that the intended answer would involve a design that didn't involve a "pendulum" effect (as shown in the illustration due to the weight of the "hanging" control stick) acting to hold the elevator in a horizontal position when the fuselage is at rest.  The problem with a "pendulum" design, as noted in another answer to this ASE question, is that it creates a connection between the fuselage pitch attitude in steady-state flight, and the trim position of the elevator.  The elevator will tend to trim higher (causing a nose-up control input) when the aircraft is climbing than when it is descending.  This means that adding power will tend to cause the elevator to rise.  This is generally not desirable.
If for some reason it is deemed desirable that the elevator remain horizontal when the aircraft is at rest on the ground with no one at the controls -- and it's debatable whether this a really a characteristic of a "correctly designed control system"-- then a re-design could use a control yoke rather than a control stick, or could use a lightweight control stick mounted in the conventional way, and could use springs to hold the elevator in a horizontal position.  Proper "balancing" of the elevator in relation to the hinge line or pivot point could minimize the amount of spring force needed to accomplish this.
All things considered, it's a very poor homework question.  The use of the word "steering" is objectionable, as is the statement that the plane is "on the runway" (apparently should read "ramp" or "tarmac" or "parking area"),  and rather than specifying a "correctly designed" control system, the question ought to specify what design objectives should be met, that are lacking in the design shown in the diagram.

+1 for "it's a very poor homework question". And since it is a homework question with no sign of effort from the OP, I'd offer my general appeal. Although the assigned question itself is such a mess, this isn't quite the same as a question asking for a computation.